Rob,

One source of undamped decay that isn't much talked about is how rigid is 
the support for the top wire connection.  Much energy can be absorbed by 
microscopic swaying of the support.  Similarly, if the base is mounted on 
something less rigid than bedrock, energy might be getting absorbed by the 
mounting surface.  Air damping is a small effect, but it could be a 
factor.  And, of course, there is pivot quality, which has already been 
much discussed.  Also, if you have a coil on the boom, it should be 
open-circuited to avoid losses due to interaction with the local magnetic 
field.

Once you have minimized all those effects, you will then want to add back a 
good amount of well behaved damping such as with Chris' magnetic 
array.  You probably don't want your Lehman to just respond to one 
frequency, but would prefer it to have a range of frequencies which it will 
respond to.  That is what you will get when you use relatively strong 
damping.  Reduced sensitivity = increased band width.

Brett

At 08:26 AM 4/18/2009 -0700, you wrote:
>Gary,
>
>I am curious.
>
>What are typical times for Lehman half-life decay?
>
>What are the main causes  of decay?
>
>Rob


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